Communication system, base station control device, and base station device

ABSTRACT

There are provided a communication system, a base station control device, and a base station device capable of improving communication quality. In the communication system ( 100 ), the base station control device ( 120 ) totalizes information on the number of base stations as the number of base station devices ( 130 ) which can communicate with a mobile station device ( 140 ), makes Nb copies of a data frame, successively assigns integer values from 1 to Nb as stream numbers Ns to the data frames copied, and forms Nb copied data frames including Nb and Ns in header information. Copied data frames having different Ns in the header information are sent to the base station devices ( 130 ) which can communicate with the mobile station device ( 140 ). According to the Ns and Nb contained in the copied data frame, the base station device ( 130 ) subjects the data in the copied data frame to temporal/spatial encoding to form a temporal/spatial encoding series. The mobile station device ( 140 ) receives the temporal/spatial encoding series signal from each of the base station devices ( 130 ).

This is a continuation application of application Ser. No. 11/573,536filed Feb. 9, 2007, which is a national stage of PCT/JP2005/013849 filedJul. 28, 2005, which is based on Japanese Application No. 2004-234523filed Aug. 11, 2004 and Japanese Application No. 2005-207800 filed Jul.15, 2005, the entire contents of each which are incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to a communication system, to a basestation control apparatus, and to a base station apparatus, andparticularly relates to a base station apparatus, to a base stationcontrol apparatus for controlling the base station apparatus, and to acommunication system that is provided with a plurality of base stationapparatuses and base station control apparatuses.

BACKGROUND ART

A conventional radio communication system that has a base stationcontrol apparatus uses a macrodiversity technique to obtain diversityeffects by transmitting data in the same path from a plurality of basestation apparatuses to a certain mobile station apparatus. In a radiocommunication system that uses the CDMA (Code Division Multiple Access)system in IMT-2000, a diversity communication technique is introducedwhereby a base station control apparatus transmits sound, packets,control information, and other signals to a single mobile stationapparatus via a plurality of base station apparatuses. This techniqueensures high-quality communication through a diversity benefit that isobtained by a process in which the transmission signal is duplicated inthe base station control apparatus, and the duplicated transmissionsignal is transmitted in parallel to the plurality of base stationapparatuses via a plurality of wire transmission lines, and thentransmitted from the plurality of base station apparatuses to the mobilestation apparatus via a radio propagation channel.

FIG. 1 is a block diagram showing the structure of the conventionalradio communication system 10. As shown in FIG. 1, the conventionalradio communication system 10 has a core network 11, base stationcontrol apparatus 12, a plurality of base station apparatuses 13-1,13-2, and mobile station apparatus 14. The system has the same structurewhen there are two or more base station apparatuses 13.

Core network 11 and base station control apparatus 12 are connected bywire transmission line 15, and each of the plurality of base stationapparatuses 13-1, 13-2 is independently connected to base stationcontrol apparatus 12 by wired transmission lines 16-1, 16-2,respectively. Mobile station apparatus 14 also communicates with theplurality of base station apparatuses 13-1, 13-2 via radio propagationchannel 17-1, 17-2, respectively.

Following is a description of the operations that occur when data aretransmitted from core network 11 to mobile station apparatus 14 in thetype of structure described above.

First, core network 11 transmits a data frame to base station controlapparatus 12 via wired transmission line 15. Base station controlapparatus 12 that receives the data frame duplicates the received dataframe for transmission to the plurality of base station apparatuses13-1, 13-2 and transmits the duplicated data frame to base stationapparatuses 13-1, 13-2 via wired transmission lines 16-1, 16-2,respectively.

The plurality of base station apparatuses 13-1, 13-2 adds controlinformation to the received data frames to form radio frames, andtransmits the radio frames to mobile station apparatus 14 via radiopropagation channels 17-1, 17-2.

Next, in mobile station apparatus 14, the transmission lag in radiopropagation channels 17-1, 17-2 between the received radio frames iscorrected, the phases of the radio frames are aligned, the radio framesare synthesized, and the received data are reconstructed from thesynthesized signals.

In the conventional radio communication system 10 described above,higher quality communication is achieved by causing mobile stationapparatus 14 to receive the same data frames via a plurality of radiopropagation channels 17-1, 17-2. Even when phasing or another factor isin effect, e.g., when the propagation environment of the first radiopropagation channel 17-1 has deteriorated, higher quality communicationcan still be achieved by synthesizing the data frame received via theother radio propagation channels 17-2.

-   Non-patent Document 1: 3GPP TS 25.427 UTRAN Iub/Iur Interface User    Plane Protocol For DCH Data Streams

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, signals transmitted from a plurality of base stations in theconventional communication system are sometimes in a phase relationshipin which the signals cancel each other out under some conditions of thepropagation path. In this case, adequate characteristics are notobtained, and the communication quality is inadequate. The conventionalcommunication system also has drawbacks in that an adequate receptionlevel is not obtained in the mobile station apparatus at cell edges thatare distant from the base station apparatus.

An object of the present invention is to provide a communication system,a base station control apparatus, and a base station apparatus thatimprove communication quality.

Means for Solving the Problem

A first aspect of the present invention resides in a communicationsystem comprising a base station control section including a copyingsection that forms N (a natural number equal to 2 or higher) is sets ofcopied data by copying transmission data, a control information additionsection that adds control information relating to channel encoding to aheader portion of each set of copied data, and a transmission sectionthat transmits to separate base station apparatus each of the sets ofcopied data the control information is added to; and base stationapparatuses that each have a control information extraction section thatextracts the control information from the copied data, and an encodingsection that forms an encoding series signal for which channel encodingis performed according to the extracted control information.

A second aspect of the present invention resides in a base stationapparatus comprising a control information extraction section forextracting control information relating to channel encoding from aheader portion of a data frame; a pilot symbol addition section thatadds a known pilot symbol to a transmission signal; and an encodingsection that forms, according to the extracted control information, anencoding series signal from the transmission signal that includes apilot signal.

A third aspect of the present invention resides in a base stationcontrol apparatus comprising a copying section that forms N sets ofcopied data by copying transmission data, a control information additionsection that adds control information to a header portion of each set ofcopied data, and a transmission section that transmits, to separate basestation apparatus, each of the sets of copied data the controlinformation is added to.

Advantageous Effect of the Invention

The present invention provides a communication system, a base stationcontrol apparatus, and a base station apparatus that are capable ofimproving communication quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the overall structure of the conventionalradio communication system;

FIG. 2 is a block diagram showing the structure of the radiocommunication system according to Embodiment 1 of the present invention;

FIG. 3 is a diagram showing the control flow relating to detection ofthe transmission time difference between base station apparatuses when adownlink transmission signal transmitted from the base stationapparatuses to a mobile station apparatus is used as the transmissionsignal;

FIG. 4 is a diagram showing the control flow relating to detection ofthe reception level and reception quality when a downlink transmissionsignal transmitted from the base station apparatuses to a mobile stationapparatus is used as the transmission signal;

FIG. 5 is a block diagram showing the structure of the radiocommunication system according to Embodiment 2 of the present invention;

FIG. 6 is a block diagram showing the structure of the radiocommunication system according to Embodiment 3 of the present invention;and

FIG. 7 is a flowchart showing the operation of switching space-timeencoding transmission and spatial multiplexing transmission.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detailhereinafter with reference to the accompanying drawings. The samereference symbols are used to indicate structural elements that are thesame in the embodiments, and no redundant descriptions of these elementsare given.

Embodiment 1

As shown in FIG. 2, the radio communication system 100 of the presentembodiment is provided with core network 110, base station controlstation apparatus 120, a plurality of base station apparatuses 130-1,130-2, and mobile station apparatus 140. In the embodiments, cases aredescribed in which the number Nc of base station apparatuses provided tothe radio communication system is 2, but the same structure is formedwhen the Nc is greater than 2.

Core network 110 and base station control station apparatus 120 areconnected by wired transmission line 150, and each of the plurality ofbase station apparatuses 130-1, 130-2 is independently connected to basestation control apparatus 120 by wired transmission lines 160-1, 160-2,respectively.

Further, mobile station apparatus 140 communicates with the plurality ofbase station apparatuses 130-1, 130-2 via radio propagation channels170-1, 170-2, respectively.

Base station control apparatus 120 is provided with IF (interface)section 121, transmission control section 122 provided to a user channelunit, transmission frame formation control section 123, controlinformation assigning section 124, copying section 125, and base stationIF section 126.

IF section 121 receives data that are transmitted from core network 110via wired transmission line 150, and extracts a data frame from thereceived data.

Transmission control section 122 outputs the data frame extracted by IFsection 121 to control information assigning section 124 each time apre-set time period elapses. When there is no data frame to beoutputted, information indicating the absence of data is outputted.

Transmission frame formation control section 123 communicates with basestation apparatuses 130, acquires communication enabled/disabledinformation from each of base station apparatuses 130 via base stationIF section 126, totalizes base station number information Nb thatindicates the number of base station apparatuses 130 capable ofcommunicating with mobile station apparatus 140, outputs the basestation number information Nb to control information assigning section124 and copying section 125, and outputs base station apparatusidentification information of base station apparatuses 130 capable ofcommunicating with mobile station apparatus 140 to copying section 125.

Control information assigning section 124 adds the base station numberinformation Nb from transmission frame formation control section 123 asheader information to the data frame transmitted from transmissioncontrol section 122, and outputs to copying section 125 the data framethus added to.

Copying section 125 makes a number of copies equal to Nb of the dataframe outputted from control information assigning section 124 on thebasis of the base station number information Nb from transmission frameformation control section 123. Stream numbers Ns that are integers from1 to Nb are assigned in sequence to the Nb copied data frames. Thestream number Ns assigned to each copied data frame is included in(added to) each set of header information, each set of base stationidentification information from transmission frame formation controlsection 123 is also added to each copied data frame, and the data framesthus added to are outputted to base station IF section 126.Specifically, copying section 125 functions not only a section thatcopies data, but also as a section that adds control information. Thestream number Ns is used when a radio frame is generated in base stationapparatus 130.

Base station IF section 126 transmits each of the Nb copied data framesas wired transmission frames via wired transmission lines 160 to basestation apparatus 130 that is indicated by the base stationidentification information added to each copied data frame.

When transmission frame formation control section 123 outputsinformation indicating that there are no data frames to be outputted,control information assigning section 124 transmits to copying section125 only the header information the base station number information Nbis added to. Copying section 125 makes a number of copies equal to Nb ofthe header information, includes in each set of header information thestream number Ns assigned to each set of header information, and addseach set of base station identification information from transmissionframe formation control section 123 to each copied set of headerinformation. The sets of header information thus added to are outputtedto base station IF section 126. Base station IF section 126 transmits,as wired transmission frames, copied data frames that have only headerinformation and no data body.

A base station apparatus 130 is provided with IF section 131, receptionbuffer section 132 for buffering a copied data frame for each userchannel, clock section 133, buffer read-out section 134 for reading outa copied data frame for each user channel in synchrony with clocksection 133, control information extraction section 135 for extractingcontrol information from a copied data frame, radio frame generationsection 136, and space-time encoding section 137.

IF section 131 transmits a wired transmission frame (copied data framein this instance) received via wired transmission line 160 to receptionbuffer section 132.

Reception buffer section 132 stores the copied data frame from IFsection 131.

Clock section 133 generates a clock signal that is synchronized with aclock in transmission control section 122 of base station controlapparatus 120, and feeds the clock signal to buffer read-out section134.

Buffer read-out section 134 reads the copied data frame stored inreception buffer section 132 in synchrony with the clock signal fromclock section 133, and transmits the copied data frame to controlinformation extraction section 135 and radio frame generation section136.

Control information extraction section 135 extracts the base stationnumber information Nb and the stream number Ns from the controlinformation included in the header of the copied data frame from bufferread-out section 134, and transmits the base station number informationNb and the stream number Ns to space-time encoding section 137.

Radio frame generation section 136 deletes the header information of thecopied data frame that was transmitted from buffer read-out section 134,extracts the data body, adds a prescribed pilot symbol and controlinformation used for the radio propagation channel to the data body, andgenerates a radio frame. The radio frame is transmitted to space-timeencoding section 137.

Radio frame generation section 136 does not generate a radio frame whenthe copied data frame from buffer read-out section 134 is composed ofonly header information and no data body. Accordingly, a radio frame isnot transmitted to mobile station apparatus 140 in this case.

space-time encoding section 137 performs the following operations usingthe output (stream number Ns and the information Nb indicating thenumber of communication-enabled base stations) of control informationextraction section 135 and the output of radio frame generation section136.

space-time encoding section 137 does not perform space-time encoding foran inputted radio frame when the base station number information Nboutputted from control information extraction section 135 is 1.Accordingly, after a prescribed communication path encoding is performedfor transmission in a radio propagation channel, the radio frame ismodulated according to a prescribed modulation method, converted to aradio frequency band, and transmitted from antenna 138.

When the base station number information Nb outputted from controlinformation extraction section 135 is 2 or higher, space-time encodingsection 137 performs communication path encoding of the inputted radioframe according to the stream number Ns to form a space-time encodingseries. The stream number Ns and the encoding method herein aredetermined in advance on the basis of a prescribed method of generatinga space-time code. A method that can be adaptively varied according tothe condition of the radio communication path may also be applied withregard to the modulation method and the encoding ratio used duringencoding.

The space-time block code, space-time trellis code, space-time turbocode, and other techniques and combinations of techniques described inthe reference B. Vucetic and J. Yuan, “Space-Time Coding,” John Wiley &Sons Ltd., may be applied in the space-time encoding performed in radiocommunication system 100.

An interleaver may also be applied along an appropriate frame length ineach of base station apparatuses 130. In this case, a common interleavermust be used for all of base station apparatuses 130.

A case will be described herein in which the space-time block codeapplied in radio communication system 100 is based on the reference S.M. Alamouti, “A simple transmit diversity technique for wirelesscommunications,” IEEE Journal Select. Areas Commun., Vol. 16, No. 8, pp.1451-1458, October 1998. The particular case described herein is one inwhich the base station number information Nb is 2.

When the base station number information Nb is 2, the stream number Nsis 1 or 2. When space-time encoding section 137 uses an M-valuemodulation method, radio frames are grouped for every log₂M bits. Whenthe stream number Ns outputted from control information extractionsection 135 is 1, space-time encoding section 137 performs space-timeencoding to form the space-time encoding series S(2m−1), −S(2m)*(whereinm=1, . . . , K/2). When the stream number Ns outputted from controlinformation extraction section 135 is 2, space-time encoding isperformed to form the space-time encoding series S(2m), S(2m−1)*(whereinm=1, . . . , K/2). The modulation symbol for the results of modulationherein is S(k) (wherein k=1, . . . , K), and the symbol “*” representsthe phase-conjugation operator in the complex phase plane.

When a space-time trellis code or a space-time turbo code is applied inradio communication system 100, space-time encoding can be achieved byperforming trellis encoding using a different generator matrix for eachstream number.

The space-time encoding series that is space-time encoded in space-timeencoding section 137 in this manner is subjected to a prescribedmodulation, converted to a radio frequency band, and transmitted fromantenna 138 to mobile station apparatus 140.

Mobile station apparatus 140 receives the plurality of space-timeencoded space-time encoding series that is transmitted from theplurality of base station apparatuses (base station apparatus 130-1 andbase station apparatus 130-2 herein).

The following routine is executed between base station apparatus 130 andmobile station apparatus 140 as a routine that is executed before theradio frame is received. Specifically, base station apparatus 130-1 orbase station apparatus 130-2 first uses a control channel to notifymobile station apparatus 140 in advance of the frame timing and theidentification information of base station apparatus 130 for performingthe space-time encoding. Upon completing preparation for receiving theframe that corresponds to the space-time encoding transmissionnotification from base station apparatus 130, mobile station apparatus140 notifies base station apparatus 130 that is the transmission sourceof notice of the base station identification information thatpreparation for reception is completed using a control channel. Thesystem of reception in mobile station apparatus 140 is thus prepared.

When reception of the radio frame is initiated, mobile station apparatus140 performs channel estimation from base station apparatuses 130 tomobile station 140 on the basis of a known pilot signal seriestransmitted from base station apparatuses 130. Mobile station apparatus140 then decodes the plurality of received radio frames using thechannel estimation values hj (wherein j=1, . . . , Nb) obtained bychannel estimation.

The specific method of receiving the signal that is encoded byspace-time block encoding, space-time trellis encoding, space-time turboencoding, or another technique or combination of the aforementionedtechniques is described, for example, in B. Vucetic, J. Yuan,“Space-Time Coding,” John Wiley & Sons Ltd., and will not be describedherein.

In radio communication system 100, the base station number informationNb and the stream number Ns are included in the header of each wiredtransmission frame in base station control apparatus 120 and aretransmitted to base station apparatuses 130, but the present inventionis not limited to this configuration. A configuration may also beadopted in which the pair composed of the stream number Ns and thenumber Nb of base stations that can communicate is correlated with pairidentification information, and the pair identification information isincluded in the header of the wired transmission frame and transmittedto base station apparatuses 130. In this case, a table in which thepairs of base station numbers Nb and stream numbers Ns are correlatedwith pair identification information must be stored in advance in basestation apparatuses 130. Control information extraction section 135extracts the pair identification information included in the header of asub-data frame that is outputted from buffer read-out section 134,references the abovementioned table using the pair identificationinformation as a key, and outputs the corresponding base station numberNb and stream number Ns to space-time encoding section 137.

In radio communication system 100, base station control apparatus 120and the plurality of base station apparatuses 130 perform synchronizedtransmission operations, but the radio propagation channel between theplurality of base station apparatuses 130 and mobile station apparatus140 generally is different. Therefore, a difference occurs in the timeat which the transmission signals from the plurality of base stationapparatuses 130 reach mobile station apparatus 140.

Since the characteristics of the space-time encoding are expected todeteriorate when the time difference can no longer be ignored withrespect to the symbol interval, base station control apparatus 120controls the reception timing among base station apparatuses 130 so thatthe timing at which the space-time encoding series transmitted from eachof base station apparatuses 130 are received by mobile station apparatus140 is within a prescribed time difference. It is thereby possible toprevent the abovementioned characteristics from deteriorating due todeviations in the reception timing.

As a method for placing the reception timing of the space-time encodingseries within a prescribed time difference in mobile station apparatus140, the timing at which radio frames are transmitted is synchronizedbetween base station apparatus 130-1 and base station apparatus 130-2,in which case mobile station apparatus 140 transmits the same signal tobase station apparatus 130-1 and to base station apparatus 130-2 anddetects the difference in the timing at which the signals reach basestation apparatus 130-1 and base station apparatus 130-2. The timing ofreception in mobile station apparatus 140 can then be placed within theprescribed time difference by controlling the timing at which basestation IF section 126 of base station control apparatus 120 sendscopied data frames to base station apparatuses 130 based on the timingdifference detected in base station apparatus 130.

The method disclosed in Japanese Patent No. 3296822 that uses atransmission signal in a downlink may also be used to detect atransmission time difference between base stations.

FIG. 3 is a diagram showing the control flow relating to detection ofthe transmission time difference between base station apparatuses when adownlink transmission signal transmitted from base station apparatuses130 to mobile station apparatus 140 is used as the transmission signal.

Base station apparatus 130-1 or base station apparatus 130-2 firstestablishes a link to mobile station apparatus 140 (step ST401).

Mobile station apparatus 140 then measures the reception strength of thetransmission signal that is transmitted from base station apparatus130-1 and base station apparatus 130-2 by using a control channel, andmeasures the time difference Tn (frame offset) in the reception timingof the transmission signal transmitted from both base stationapparatuses (step ST402). The control channel is a shared controlchannel that is constantly broadcasted by base station apparatuses 130.

Notification of the results of measuring the time difference Tn inmobile station apparatus 140 is then issued to base station controlapparatus 120 through base station apparatus 130-1 or base stationapparatus 130-2 with which the link is established (step ST403). Thereception timing in mobile station apparatus 140 can be placed withinthe prescribed time difference by using the time difference Tn detectedby mobile station apparatus 140 as a basis for adjusting (step ST404)the timing at which base station IF section 126 of base station controlapparatus 120 sends copied data frames to base station apparatuses 130.

In radio communication system 100, base station control apparatus 120sets to a prescribed level the quality at which the transmission signaltransmitted from the plurality of base station apparatuses (base stationapparatus 130-1 and base station apparatus 130-2 in this ease) isreceived in mobile station apparatus 140, and performs control so thatthe difference in the reception level is within a prescribed leveldifference. Radio frames transmitted from base station apparatuses 130can thereby be decoded with good precision in mobile station apparatus140. As a result, communication quality in radio communication system100 can be enhanced.

For example, control is made possible by providing feedback to basestation apparatuses 130 of information relating to the quality and levelat which the transmission signal transmitted from base stationapparatuses 130 is received in mobile station apparatus 140.

FIG. 4 is a diagram showing the control flow relating to detection ofthe reception level and reception quality when a downlink transmissionsignal transmitted from base station apparatuses 130 to mobile stationapparatus 140 is used as the transmission signal.

Base station apparatus 130-1 or base station apparatus 130-2 firstestablishes a link to mobile station apparatus 140 (step ST501).

Mobile station apparatus 140 then measures the reception strength of thetransmission signal that is transmitted from base station apparatus130-1 and base station apparatus 130-2 by using a control channel, andmeasures the reception power difference Pn (or SIR) of the transmissionsignal transmitted from both base station apparatuses (step ST502). Thecontrol channel is a shared control channel that is constantlybroadcasted by base station apparatuses 130.

Notification of the results of measuring the reception power differencePn in mobile station apparatus 140 is then issued to base stationcontrol apparatus 120 through base station apparatus 130-1 or basestation apparatus 130-2 with which the link is established (step ST503).The reception quality in mobile station apparatus 140 can be placedwithin the prescribed level, and the difference in the reception levelcan be placed within the prescribed level difference by using thereception power difference Pn detected by mobile station apparatus 140as a basis upon which base station control apparatus 120 controls (stepST504) the transmission power of space-time encoding section 137 of eachof base station apparatuses 130.

In radio communication system 100 of the present embodiment, the basestation number information Nb that is the number of base stationapparatuses 130 capable of communicating with mobile station apparatus140 is totalized in base station control apparatus 120, a number ofcopies equal to Nb are made of a data frame, an integer from 1 to Nb isassigned in sequence as a stream number Ns to each copied data frame,and a number of copied data frames equal to Nb are formed that includethe Nb and the Ns in header information. A copied data frame having adifference Ns in the header information is then transmitted to each ofbase station apparatuses 130 capable of communicating with mobilestation apparatus 140. In base station apparatuses 130, the data bodiesof the copied data frames are space-time encoded to form a space-timeencoding series on the basis of the Ns and Nb included in the copieddata frames that are acquired from base station control apparatus 120.

Specifically, in radio communication system 100, according to thepresent embodiment, base station control apparatus 120 forms the basestation number information Nb (a natural number equal to 2 or greater)of data frames that is the number of base station apparatuses 13 capableof communicating with mobile station apparatus 140 by copying, adds aparameter N and a stream number Ns (any integer from 1 to N) that isassigned to each set of copied data to the header portions of the copieddata frames, for transmission to separate base station apparatuses 130as the radio frames. Each of base station apparatuses 130 extracts theparameter N and the stream number Ns from the radio frame, and forms aspace-time encoding series signal that corresponds to the extractedparameter N and stream number Ns. Mobile station apparatus 140 thenreceives a space-time encoding series signal from each of base stationapparatuses 130.

Accordingly, since each of base station apparatuses 130 forms aspace-time encoding series on the basis of the control information whenbase station control apparatus 120 adds the parameter Nb and the streamnumber Ns as control information, there is no need for processing to beperformed by base station control apparatus 120 to form a space-timeencoding series. Therefore, a plurality of different base stationapparatuses 130 can be used to communicate using space-time encodingwith a reduced processing load in base station control apparatus 120.Space-time encoded transmission is also performed in which mobilestation apparatus 140 receives a space-time encoding series signal fromeach of base station apparatuses 130, whereby diversity effects areobtained, and communication quality can be enhanced. As a result,improved reception quality at cell edges can be anticipated.

The transmission signal that is transmitted by base station apparatuses130 on the basis of control information from base station controlapparatus 120 is a stream that is space-time encoded and transmittedbetween different base station apparatuses 130. Therefore, since thephase difference of each stream changes temporally, and the same phaseis not maintained, locations at which the phases cancel each other outat the time of reception by mobile station apparatus 140 changetemporally. As a result, the local dependence of the communicationquality can be reduced.

Furthermore, in radio communication system 100 of the presentembodiment, the timing at which the copied data frames are transmittedto base station apparatuses 130 is adjusted in base station controlapparatus 120 so that the timing at which the space-time encoding seriessignals from base station apparatuses 130 are received in mobile stationapparatus 140 is within the prescribed time difference.

Accordingly, the characteristics of the space-time-encoded transmissioncan be prevented from deteriorating due to deviations in the receptiontiming in mobile station apparatus 140.

In base station control apparatus 120 of radio communication system 100of the present embodiment, a transmission power control signal forcontrolling the transmission power of the encoding series signal istransmitted to base station apparatuses 130 on the basis of receptionquality information from mobile station apparatus 140 for receiving thetransmission signal transmitted from each of base station apparatuses130.

Accordingly, radio frames transmitted from base station apparatuses 130can thereby be decoded with good precision in mobile station apparatus140. As a result, communication quality in radio communication system100 can be enhanced.

Embodiment 2

The radio communication system 100A according to Embodiment 2 shown inFIG. 5 has the same overall structure as radio communication system 100shown in FIG. 2. However, the two systems are different in that basestation control apparatus 120A has a series-parallel conversion section221 instead of copying section 125 in base station control apparatus120, and base station apparatuses 130A have spatial multiplexing section231 instead of space-time encoding section 137 of base stationapparatuses 130.

In base station control apparatus 120A, series-parallel conversionsection 221 generates, on the basis of base station number informationNb from transmission frame formation control section 123, a number ofsub-data frames equal to Nb by series/parallel conversion from dataframes that are series data outputted from control information assigningsection 124. Integers from 1 to Nb are then assigned in sequence asstream numbers Ns to the sub-data frames thus generated. The streamnumber assigned to each sub-data frame is included in the headerinformation of each sub-data frame, each set of base stationidentification information outputted from transmission frame formationcontrol section 123 is added to the corresponding sub-data frame, andthe sub-data frames are outputted to base station IF section 126. Thestream number Ns is used when a radio frame is generated in a basestation apparatus and when a sub-data frame transmitted in parallel byspatial multiplexing transmission is decoded in mobile station apparatus140A to the original series data frame.

Base station IF section 126 transmits each of the Nb sub-data frames aswired transmission frames via wired transmission line 160 to basestation apparatus 130A that is indicated by the base stationidentification information added to the sub-data frames.

In base station apparatuses 130A, spatial multiplexing section 231performs the following operations using the output (information Nb as tothe number of base stations that can communicate) of control informationextraction section 135 and the output of radio frame generation section136.

spatial multiplexing section 231 does not perform spatial multiplexingtransmission of the inputted radio frames when the base station numberinformation Nb outputted from control information extraction section 135is 1. Accordingly, after a prescribed communication path encoding isperformed for transmission in a radio propagation channel, the radioframe is modulated according to a prescribed modulation method,converted to a radio frequency band, and transmitted from an antenna138.

When the base station number information Nb outputted from controlinformation extraction section 135 is 2 or higher, spatial multiplexingsection 231 performs communication path encoding of the inputted radioframe.

The stream number Ns and the encoding method herein are determined inadvance on the basis of a prescribed method of generating a space-timecode. A method that can be adaptively varied according to the conditionof the radio communication path may also be applied with regard to themodulation method and the encoding ratio used during encoding.

The radio frame that is communication-path encoded in spatialmultiplexing section 231 in this manner is subjected to a prescribedmodulation, converted to a radio frequency band, and transmitted fromantenna 138 to mobile station apparatus 140A.

Each of the Nb sub-frames that are series-parallel converted in basestation control apparatus 120A is thus transmitted from separate basestation apparatus 130A to mobile station apparatus 140A, whereby aspatial multiplexing transmission such as MIMO (Multi Input MultiOutput) can be achieved.

Mobile station apparatus 140A receives the plurality of radio framesthat is transmitted from the plurality of base station apparatuses (basestation apparatus 130A-1 and base station apparatus 130A-2 herein).

The following routine is executed between base station apparatus 130Aand mobile station apparatus 140A as a routine that is executed beforethe radio frame is received. Specifically, base station apparatus 130A-1or base station apparatus 130A-2 first uses a control channel to notifymobile station apparatus 140A in advance of the frame timing and theidentification information of base station apparatus 130A that istransmitting the radio frame. Upon completing preparation for receivingthe frame that corresponds to the notification from base stationapparatus 130A, mobile station apparatus 140A notifies base stationapparatus 130A that is the transmission source of base identificationinformation that preparation for receiving is completed using a controlchannel. The system of reception in mobile station apparatus 140A isthus prepared.

When reception of the radio frame is initiated, mobile station apparatus140A performs channel estimation from base station apparatuses 130A tomobile station 140A on the basis of a known pilot signal seriestransmitted from base station apparatuses 130A. Mobile station apparatus140A then separately receives and decodes the plurality of receivedradio frames to obtain a plurality of sub-data frames through the use ofmaximum likelihood decoding, an interference canceller, or anothermethod using the channel estimation values hj (wherein j=1, . . . , Nb)obtained by channel estimation. Decoding to the original series dataframes is performed on the basis of the stream number Ns included in theheader information of the plurality of sub-data frames.

The specific reception method is described in A. Paulraj, R. Nabar, andD. Gore, “Introduction to Space-Time Wireless Communications”, CambridgeUniversity Press, and will not be described herein.

In radio communication system 100A as well, the base station numberinformation Nb and the stream number Ns are included in the header ofeach wired transmission frame in base station control apparatus 120A andtransmitted to base station apparatuses 130A, but the present inventionis not limited to this configuration. A configuration may also beadopted in which the pair composed of the stream number Ns and thenumber Nb of base stations that can communicate is correlated with pairidentification information, and the pair identification information isincluded in the header of the wired transmission frame and transmittedto base station apparatuses 130A. In this case, a table in which thepairs of base station numbers Nb and stream numbers Ns are correlatedwith pair identification information must be stored in advance in basestation apparatuses 130A. Control information extraction section 135extracts the pair identification information included in the header of asub-data frame that is outputted from buffer read-out section 134,references the abovementioned table using the pair identificationinformation as a key, and outputs the corresponding base station numberNb and stream number Ns to spatial multiplexing section 231.

Similar to radio communication system 100, it is sometimes impossible inradio communication system 100A to ignore the difference in the times atwhich the transmission signals transmitted from the plurality of basestation apparatuses 130A reach mobile station apparatus 140A withrespect to the symbol timing, and the characteristics of the spatialmultiplexing transmission are expected to deteriorate in this case. Thecharacteristics of spatial multiplexing in radio communication system100A can be prevented from deteriorating by applying the methoddescribed in Embodiment 1 whereby the reception timing of the radioframes is brought to within a prescribed time difference.

Radio communication system 100A may also utilize the method of controldescribed in Embodiment 1 whereby the reception quality of thetransmission signal transmitted from the plurality of base stationapparatuses to mobile station apparatus 140A is brought to a prescribedlevel, and the difference in reception levels is brought to within aprescribed level difference.

In radio communication system 100A of the present embodiment, seriesdata frames are converted to a parallel series to form a number ofsub-data frames equal to Nb, an integer from 1 to Nb is assigned insequence as a stream number Ns to each of the sub-frames, and Nbsub-frames in which the Nb and the Ns are included in (added to) headerinformation are formed in base station control apparatus 120A. In basestation apparatuses 130A, spatial-multiplex-transmitted frames areformed on the basis of sub-frames acquired from base station controlapparatus 120A. The transmission frames transmitted from each of basestation apparatuses 130A are received by mobile station apparatus 140A.

Because spatial multiplexing transmission can be performed betweenmobile station apparatus 140A and the plurality of base stationapparatuses 130A, the transmission rate can be enhanced. As a result,throughput in radio communication system 100A can be enhanced.

In the description of Embodiment 2, a single stream for each basestation apparatus is transmitted using a single antenna when spatialmultiplexing transmission from communication-enabled base stationapparatuses 130 is performed using a plurality of base stationapparatuses. However, this configuration is not limiting, and when thecommunication-enabled base station apparatuses 130 have a plurality ofantennas and can transmit a plurality of streams, a directional beam mayalso be formed to transmit the stream assigned to a certain base stationapparatus 130. Improved communication quality can be anticipated byenhancing the directional gain in this manner.

The plurality of streams may also be transmitted from a single basestation apparatus 130 after space-time encoding is performed. It isthereby possible to take advantage of the spatial degree of freedom ofeach of base station apparatuses 130 that can communicate, therebyresulting in an even further increase in the spatial diversity effect oftransmission.

Embodiment 3

Radio communication system 100B of Embodiment 3 shown in FIG. 6 has thesame overall structure as radio communication system 100 shown in FIG.2. However, base station control apparatus 120B has frame formationsection 321, and frame formation section 321 has series-parallelconversion section 221 in addition to copying section 125. Further, thebase station apparatuses 130B have radio frame processing section 331,and radio frame processing section 331 has spatial multiplexing section231 in addition to space-time encoding section 137.

Radio communication system 100B is characterized in switching space-timeencoding transmission and spatial multiplexing transmission using theplurality of base station apparatuses 130B according to the conditionsof a wireless propagation channel between base station apparatuses 130Band mobile station apparatus 140B.

The operation of switching space-time encoding transmission and spatialmultiplexing transmission in radio communication system 100B will firstbe described.

As shown in FIG. 7, base station apparatus 130B-1 or base stationapparatus 130B-2 first establishes a link to mobile station apparatus140B (step ST601).

Mobile station apparatus 140B then measures the reception strength ofthe transmission signal that is transmitted from base station apparatus130B-1 and base station apparatus 130B-2 by using a control channel anddetermines the reception quality (or SIR) of the transmission signalfrom both base station apparatuses (step ST602).

Mobile station apparatus 140B then notifies, through base stationapparatus 130B-1 or base station apparatus 130B-2 with which the link isestablished, base station control apparatus 120B of the receptionquality of the transmission signal from base station apparatuses 130B(step ST603). The control channel is a shared control channel that isconstantly broadcasted by base station apparatuses 130B.

In base station control apparatus 120B, transmission frame formationcontrol section 123B then determines whether every reception qualityacquired from mobile station apparatus 140B exceeds a prescribed levelof reception quality (step ST604).

When every reception quality exceeds the prescribed level of receptionquality (step ST604: YES), transmission frame formation control section123B performs control for switching to a spatial multiplexingtransmission mode (step ST605). When the reception qualities includeones that do not exceeds the prescribed level of reception quality (stepST604: NO), transmission frame formation control section 123B performscontrol for switching to a space-time encoding transmission mode (stepST606).

Specifically, when every reception quality exceeds the prescribed levelof reception quality (step ST604: YES), transmission frame formationcontrol section 123B transmits spatial multiplexing transmissionselection information for selecting spatial multiplexing transmission tocontrol information assigning section 124B and frame formation section321.

When the reception qualities include those that do not exceed theprescribed level of reception quality (step ST604: NO), transmissionframe formation control section 123B transmits space-time encodingtransmission selection information for selecting space-time encodingtransmission to control information assigning section 124B and frameformation section 321.

Control information assigning section 124B adds, to the data frametransmitted from transmission control section 122, the space-timeencoding selection information or spatial multiplexing transmissionselection information as header information in addition to the basestation number information Nb from transmission frame formation controlsection 123B, and transmits the data frame to frame formation section321.

In frame formation section 321, space-time encoding transmissionselection information is acquired from transmission frame formationcontrol section 123B, whereupon copying section 125 makes Nb copies ofthe data frame the space-time encoding transmission selectioninformation is added to as header information acquired from controlinformation assigning section 124B. A stream number assigned to eachcopied data frame is included in the sets of header information, eachset of base station identification information from transmission frameformation control section 123B is also added to each copied data frame,and the data frames thus added to are outputted to base station IFsection 126.

In frame formation section 321, spatial multiplexing transmissionselection information is acquired from transmission frame formationcontrol section 123B, whereupon series-parallel conversion section 221generates Nb sub-data frames by series/parallel conversion. The framesare generated from data frames the spatial multiplexing transmissionselection information is added to as header information acquired fromcontrol information assigning section 124B. The stream number assignedto each sub-data frame is included in header information of eachsub-data frame, each set of base station identification informationoutputted from transmission frame formation control section 123B isadded to the corresponding sub-data frame, and the sub-data frames areoutputted to base station IF section 126.

Space-time encoding transmission or spatial multiplexing transmission isthus selected on the basis of reception quality that transmission frameformation control section 123B acquires from mobile station apparatus140B and that indicates the propagation environment betweencommunication-enabled base station apparatuses 130B and mobile stationapparatus 140B, and copying section 125 or series-parallel conversionsection 221 operates based on the selection information. Space-timeencoding transmission and spatial multiplexing transmission are therebyadaptively switched.

The base station apparatuses 130B then receive a wired transmissionframe in which spatial multiplexing transmission selection informationor space-time encoding transmission selection information is included asheader information in control information assigning section 124B.Control information extraction section 135 then extracts the spatialmultiplexing transmission selection information or space-time encodingtransmission selection information, and when the selection informationincluded in the header is space-time encoding transmission selectioninformation, a command signal that causes space-time encoding section137 to operate is transmitted to radio frame processing section 331.When the selection information included in the header is spatialmultiplexing transmission selection information, a command signal istransmitted that spatial multiplexing section 231 to operate.

space-time encoding section 137 and spatial multiplexing section 231operate by receiving, from control information extraction section 135, acommand signal that causes space-time encoding section 137 or spatialmultiplexing section 231 to operate. Space-time encoding transmissionand spatial multiplexing transmission are thereby switched.

Similar to radio communication system 100, it is sometimes impossible inradio communication system 100B to ignore the difference in the times atwhich the transmission signals transmitted from the plurality of basestation apparatuses 130B reach mobile station apparatus 140B withrespect to the symbol timing, and the characteristics of space-timeencoding transmission and spatial multiplexing transmission are expectedto deteriorate in this case. The characteristics of space-time encodingtransmission and spatial multiplexing transmission in radiocommunication system 100B can be prevented from deteriorating byapplying the method described in Embodiment 1 whereby the receptiontiming of the radio frames is brought to within a prescribed timedifference.

Radio communication system 100B may also utilize the method of controldescribed in Embodiment 1 whereby the reception quality of thetransmission signal transmitted from the plurality of base stationapparatuses to mobile station apparatus 140B is brought to a prescribedlevel, and the difference in reception levels is brought to within aprescribed level difference.

In base station control apparatus 120B in radio communication system100B of the present embodiment, space-time encoding transmission orspatial multiplexing transmission is selected based on a receptionquality that indicates the propagation environment between mobilestation apparatus 140B and base station apparatuses 130B, and thisselection information is the basis upon which copying section 125 orseries-parallel conversion section 221 forms a wired transmission framefor transmission to base station apparatuses 130B. Specifically, whenthe reception quality is good, spatial multiplexing transmission isselected, and copying section 125 operates. When the reception qualityis poor, space-time encoding transmission information is selected, andseries-parallel conversion section 221 operates.

Space-time encoding transmission information or spatial multiplexingtransmission information is included as switching control information inthe header of the wired transmission data frame that is transmitted frombase station control apparatus 120B to base station apparatuses 130B.

In base station apparatuses 130B, space-time encoding section 137 orspatial multiplexing section 231 operates based on the space-timeencoding transmission information or spatial multiplexing transmissioninformation that is the switching control information included in theheader.

Specifically, in radio communication system 100B, adaptive switching ofspace-time encoding transmission and spatial multiplexing transmissionis performed based on the propagation environment between base stationapparatuses 130B and mobile station apparatus 140B. Specifically, whenthe propagation environment is favorable, a switch to space-timeencoding transmission is made, and when the propagation environment isunfavorable, a switch to spatial multiplexing transmission is made.

Accordingly, spatial multiplexing transmission in which an enhancedtransmission rate can be expected is performed when the propagationenvironment is favorable, and space-time encoding transmission isperformed when the propagation environment is unfavorable and thereception quality is reduced. The communication quality of the system asa whole is therefore enhanced, and the throughput can be increased.

In the description of the present embodiment, switching betweenspace-time encoding transmission and spatial multiplexing transmissionwas controlled according to the propagation environment, but a routinetailored to the QoS of transmission data for the mobile stationapparatus may be added as another control method. In this case, controlmay be added for performing space-time encoding transmission rather thanspatial multiplexing transmission even when the propagation environmentis favorable in such cases as when the required rate of transmissiondata is low, the transmission data are not real-time data, or the amountof data to be transmitted is small. The transmission power required fromthe base station apparatuses can thereby be reduced, and the amount ofinterference imparted to other cells can be reduced, thus contributingto improved throughput in the whole system.

Other Embodiments

(1) In the description of Embodiment 1 and Embodiment 3, a singlespace-time-encoded stream was transmitted by a single antenna from thecommunication-enabled base station apparatuses 130. However, the presentinvention is not limited by this configuration, and when thecommunication-enabled base station apparatuses 130 have a plurality ofantennas, directional properties may be formed so that transmission of aspace-time-encoded signal series is directed towards the desired mobilestation apparatus 140. Improved communication quality can be anticipatedby enhancing the directional gain in this case.

(2) In the description of Embodiment 1, a single space-time-encodedstream was transmitted from the communication-enabled base stationapparatuses 130. However, the present invention is not limited by thisconfiguration, and when the communication-enabled base stationapparatuses 130 have a plurality of antennas and can transmit aplurality of streams, a plurality of space-time-encoded streams may betransmitted from a single base station apparatus 130. It is therebypossible to take advantage of the spatial degree of freedom of each ofbase station apparatuses 130 that can communicate, thereby resulting inan even further increase in the spatial diversity effect oftransmission.

In a specific description with reference to FIG. 2, transmission frameformation control section 123 of base station control apparatus 120communicates with base station apparatus 130 and totalizer the numberNm(k) of transmittable streams in all of base station apparatuses 130-1to 130-Nb that can communicate via base station IF section 126. TheNm(k) herein is the number of transmittable streams in the kthcommunication-enabled base station apparatus 130-k, wherein k is anatural number from 1 to Nb.

As a result, when the total NL of Nm(k) exceeds Nb, at least one of thecommunication-enabled base station apparatuses 130 is capable oftransmitting a plurality of streams.

In such cases, copying section 125, based on the base station numberinformation NL from transmission frame formation control section 123,makes NL copies of the data frame outputted from control informationassigning section 124. An integer from 1 to NL is uniquely assigned inan amount of Nm(k) as a stream number Ns in sequence to the data framesthat are transmitted to the kth base station apparatus 130-k and thatare the NL copies of the data frame. The stream number Ns assigned toeach copied data frame is included in (added to) each set of headerinformation, each set of base station identification information fromtransmission frame formation control section 123 is also added to eachcopied data frame, and the data frames thus added to are outputted tobase station IF section 126. A plurality of stream numbers thatcorresponds to the number of sets of header information is included inthe header information of the copied data frames sent to base stationapparatuses 130 that transmit the abovementioned plurality of streams.

In base station apparatus 130, control information extraction section135 extracts the base station number information NL and the streamnumber Ns from the control information included in the header of thecopied data frame from buffer read-out section 134, and transmits thebase station number information NL and the stream number Ns tospace-time encoding section 137. Radio frame generation section 136deletes the header information of the copied data frame that wastransmitted from buffer read-out section 134, extracts the data body,adds a prescribed pilot symbol and control information used for theradio propagation channel to the data body, and generates a radio frame.The radio frame is transmitted to space-time encoding section 137.

space-time encoding section 137 performs the following operations byusing the output (stream number Ns and the information NL indicating thenumber of communication-enabled base stations) of control informationextraction section 135 and the output of radio frame generation section136.

Specifically, space-time encoding section 137 does not performspace-time encoding for an inputted radio frame when the base stationnumber information NL outputted from control information extractionsection 135 is 1. Accordingly, after a prescribed communication pathencoding is performed for transmission in a radio propagation channel,the radio frame is modulated according to a prescribed modulationmethod, converted to a radio frequency band, and transmitted fromantenna 138.

When the base station number information NL outputted from controlinformation extraction section 135 is 2 or higher, space-time encodingsection 137 performs channel encoding of the inputted radio frameaccording to the stream number Ns and forms a space-time encodingseries. However, when there is a plurality of stream numbers assigned,i.e., when base station apparatus 130 transmits a plurality of streams,base station apparatus 130 generates and transmits a plurality ofspace-time encoding series on the basis of a predetermined method ofgenerating a space-time encoding.

When a plurality of encoded streams is transmitted from base stationapparatus 130, the base station number information Nb and the streamnumber Ns are each included in the header of the wired transmissionframe, and the wired transmission frame is transmitted to base stationapparatus 130. However, the present invention is not limited by thisconfiguration, and a configuration may also be adopted in which the paircomposed of the stream number Ns (one or a plurality of stream numbersNs) and the number NL of base stations that can communicate iscorrelated with pair identification information, and the pairidentification information is included in the header of the wiredtransmission frame and transmitted to base station apparatuses 130. Inthis case, a table in which the pairs of base station numbers NL andstream numbers Ns are correlated with pair identification informationmust be stored in advance in base station apparatuses 130. Controlinformation extraction section 135 extracts the pair identificationinformation included in the header of a sub-data frame that is outputtedfrom buffer read-out section 134, references the abovementioned tableusing the pair identification information as a key, and outputs thecorresponding base station number Nb and stream number Ns to space-timeencoding section 137.

(3) In Embodiment 1 and Embodiment 3, base station apparatuses 130transmitted a space-time-encoded signal series using space-time encodingsection 137, but when a multi-carrier transmission such as OFDM is used,a spatial frequency encoding section may be provided instead ofspace-time encoding section 137 and used to transmit aspatial-frequency-encoded signal series. The encoding thus performedvaries in the sub-carrier direction instead of the temporal axisdirection, and the effects that can be obtained are the same as theeffects of using space-time encoding. A disclosure relating to spatialfrequency encoding is found in K. F. Lee and D. B. Williams,“Space-Frequency Transmitter Diversity Technique for OFDM Systems,” IEEEGlobecom 2000, Vol. 3, 2000, pp. 1473-1477, and a detailed descriptionof spatial frequency encoding will not be given herein.

The present application is based on Japanese Patent Application No.2004-234523, filed on 11 Aug. 2004, and Japanese Patent Application No.2005-207800 filed on 15 Jul. 2005, the entire content of which isexpressly incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present invention can be used as a communication system, a basestation control apparatus, and a base station apparatus that enhancecommunication quality.

1. A base station apparatus comprising: an encoding section thatgenerates an encoding sequence signal from a transmission signal; and atransmission section that transmits the encoding sequence signal as oneor more streams, wherein: the encoding section generates the encodingsequence signal using control information relating to encoding which thebase station apparatus performs in conjunction with one or more otherbase station apparatuses; and the control information is informationrelating to the one or more streams which the base station apparatustransmits.
 2. The base station apparatus according to claim 1, whereinthe control information is information relating to a quantity of the oneor more streams which the base station apparatus transmits.
 3. The basestation apparatus according to claim 2, wherein information relating tothe quantity of the one or more streams which the base station apparatustransmits is information obtained using a stream number that is assignedto each base station apparatus.
 4. The base station apparatus accordingto claim 1, wherein the encoding section generates an encoding sequencesignal that is space-time-encoded from the transmission signal using thecontrol information.
 5. The base station apparatus according to claim 2,wherein, when the quantity of the one or more streams is plural, theencoding section generates an encoding sequence signal that isspace-time-encoded, from the transmission signal.
 6. The base stationapparatus according to claim 1, wherein the encoding section generatesan encoding series signal that is spatial-frequency encoded, from thetransmission signal, using the control information.
 7. The base stationapparatus according to claim 2, wherein, when the quantity of the one ormore streams is plural, the encoding section generates an encodingseries signal that is spatial-frequency encoded, from the transmissionsignal.
 8. The base station apparatus according to claim 1, wherein thecontrol information further includes information relating tocommunication-enabled base station apparatuses.
 9. The base stationapparatus according to claim 1, wherein the control information furtherincludes a quantity of communication-enabled base station apparatuses.10. The base station apparatus according to claim 1, wherein the one ormore streams includes a known pilot symbol.
 11. The base stationapparatus according to claim 1, further comprising a spatialmultiplexing section that generates the transmission signal into aspatial-multiplex-transmitted transmission signal that is spatiallymultiplexed, wherein the encoding section and the spatial multiplexingsection are switched based on information relating to a propagationenvironment between the base station apparatus and a mobile stationapparatus.
 12. A transmission signal forming method comprising: anencoding step of generating an encoding sequence signal from atransmission signal; and a transmission step of transmitting theencoding sequence signal as one or more streams, wherein: in theencoding step, the encoding sequence signal is generated using controlinformation relating to encoding which a base station apparatus performsin conjunction with one or more other base station apparatuses; and thecontrol information is information relating to the one or more streamswhich the base station apparatus transmits.